Joining of porous silicon carbide bodies

Abstract

A method of joining two porous bodies of silicon carbide is disclosed. It entails utilizing an aqueous slip of a similar silicon carbide as was used to form the porous bodies, including the sintering aids, and a binder to initially join the porous bodies together. Then the composite structure is subjected to cold isostatic pressing to form a joint having good handling strength. Then the composite structure is subjected to pressureless sintering to form the final strong bond. Optionally, after the sintering the structure is subjected to hot isostatic pressing to further improve the joint and densify the structure. The result is a composite structure in which the joint is almost indistinguishable from the silicon carbide pieces which it joins.

What is claimed is: 
     
       1. A method of joining two porous sinterable silicon carbide bodies to each other which comprises (i) forming an aqueous slip having a silicon carbide composition which is essentially the same as that used to form the bodies to be joined in combination with at least one sintering aid and a binder which during sintering will burn out and leave essentially no residues, (ii) placing the two bodies to be joined in close proximity to each other to form an interstice there between and filling the interstice with said slip to form a composite structure, (iii) subjecting the composite structure to cold isostatic pressing to form a joint having good handling strength, and (iv) sintering the pressed structure to densify it to at least 90% of theoretical density. 
     
     
       2. The method of claim 1 wherein the porous silicon carbide bodies contain at least about 35% porosity. 
     
     
       3. The method of claim wherein the porous silicon carbide bodies contain about 35 to about 50 percent porosity. 
     
     
       4. The method of claim 1 wherein alpha-silicon carbide is used to form both the bodies and the slip. 
     
     
       5. The method of claim 1 wherein beta-silicon carbide is used to form both the bodies and the slip. 
     
     
       6. The method of claim 1 wherein the binder is selected from the group consisting of waxes, thermosetting resins, gums, polyvinyl alcohols, methyl cellulose, thermoplastic resins and mixtures thereof. 
     
     
       7. The method of claim 6 wherein the binder is a poly(ethyl oxyazaline). 
     
     
       8. The method of claim 1 wherein the sintering aid in the slip is present in an amount of about 50 to about 200% of its content in the porous bodies. 
     
     
       9. The method of claim 8 wherein the sintering aid is a combination of boron and carbon. 
     
     
       10. The method of claim 1 wherein the slip further comprises a surfactant. 
     
     
       11. The method of claim 1 wherein the slip has a solids content of about 40 to about 60 weight percent. 
     
     
       12. The method of claim 1 wherein the slip has a solids content of about 52 to about 56 weight percent. 
     
     
       13. The method of claim 1 wherein the cold isostatic pressing is conducted at a pressure of at least about 25,000 psi. 
     
     
       14. The method of claim 1 wherein the cold isostatic pressing is conducted at a pressure of at least about 40,000 psi. 
     
     
       15. The method of claim 1 wherein the cold isostatic pressing is conducted at a pressure of at least about 50,000 psi. 
     
     
       16. The method of claim 1 wherein the sintering is performed at a temperature of at least about 2050 C. for at least about 30 minutes. 
     
     
       17. The method of claim wherein after sintering the joined structure is subjected to hot isostatic pressing. 
     
     
       18. The method of claim 17 wherein the hot isostatic pressing is conducted at a temperature of at least about 1700 C. and a pressure of at least about 22,000 psi for at least about 30 minutes. 
     
     
       19. The method of claim 17 wherein the hot isostatic pressing is conducted in a manner which precludes any gas or other species from entering the joint. 
     
     
       20. The method of claim 19 wherein the manner for precluding is sealing the structure in a material selected from a tantalum can, glass, or a material which will form a glass upon heating.